The use of thermoplastic, polyester-based consumer products such as polyethylene terephthalate (PET) have become so widespread over the last few decades that they have become a fixture of modern day life. PET is used in carpet fibers, and primary and secondary carpet backings such as backing cushions. PET bottles have come to package virtually all common non-alcoholic drinks, spanning the range from water bottles to carbonated beverages to sports drinks. However, as a result of their popularity and the length of time required for the natural breakdown of the PET plastics, efforts have long been made to recycle the PET containing materials. Such recycling efforts have continued to be an important consumer consideration for several reasons. First, virgin PET is produced from petrochemicals, so that reducing the use of new bottles would lower oil consumption. Second, the recycling and reuse of recycled PET lowers emission of greenhouse gases as compared to the emissions that are generated from the extraction of oil, conversion of oil into PET intermediates, and the manufacture of final virgin PET product. Finally, recycling PET bottles or carpet and any of its components saves landfill space. Many landfills are closing, and permits for new landfills are very difficult, if not impossible, to obtain. Moreover, many high density population cities such as Seattle or New York, do not have landfill space, and consequently ship their daily waste via rail or barge, hundreds of miles to other states where landfill space is available. This space issue is a high-profile concern to modern consumers, states and municipalities, who have increasingly embraced the desirability of sustainable technologies. Indeed, such a sentiment has been demonstrated in related applications, where states such as California or cities such as New York have banned the use of plastic grocery bags or polystyrene cups. Recycling systems using a variety of mechanical or chemical processes for nylon and polypropylene-based carpet are known. However, over 95% of all PET carpeting is deposited in landfills. New and more flexible methods of recycling PET carpet components are needed to relieve the hundreds of millions of pounds of PET carpeting going into landfills today. There is thus a growing need for efficient processes to recycle PET carpet.
Current recycle methods for PET bottles typically involve the separation of colored and non-colored bottles from other recyclables and contaminants in the recycle stream. Caps, labels, adhesives and cap seals contained in the PET bottles are also removed prior to digestion in glycol, since they are made of polyolefins, not PET. Unfortunately, the purification of PET is a relatively complicated process. One manufacturer's process involves: (i) processing the bottles in a dry trommel machine to eliminate contaminants such as dirt or other particulates; (ii) treating the bottles with a magnetic field to eliminate ferromagnetic materials; (iii) washing to separate labels and adhesives from the bottles; (iv) processing the bottles through a second trommel machine to separate the PET from the labels and some of the lids; (v) auto-sorting the bottles using near-infrared detectors combined with pneumatic air streams to separate colored bottles from non-colored bottles; (vi) sorting the bottles manually to correct errors made by the near-infrared detection step; (vii) chopping the bottles into flakes; (viii) separating the polyolefin lids and seals from the higher density PET by floatation separation in water; (ix) washing the resulting PET flakes to further remove contaminants on formerly interior surfaces, labels and adhesive residues; (x) dewatering and drying to remove water; (xi) processing the flakes through a separator that removes aluminum contaminants; and optionally as a final step, (xii) melt processing the resulting flakes at high temperature in an extruder with filtering via a stainless steel screen pack to further reduce contaminants. It would be desirable to simplify this complicated process by reducing the number of steps involved, thereby making the entire process more cost effective, more environmentally friendly and more sustainable, since such streamlining would encourage even greater recycling rates throughout the world.
Following purification of the recycled PET material, a glycol digestion process may be used to convert the PET polymers to a mixture of glycols and low-molecular-weight PET oligomers. However, although such mixtures have desirably low viscosities (low molecular weight), they often have high hydroxyl numbers or high levels of free glycols.
Furthermore, digestion of recycled PET bottles without an initial separation of the polyolefin material has been disclosed, e.g., as in JP-2000-198876, JP-2004-238581 and JP-2005-002161), however, such methods can result in softened polyolefin material that agglomerates or clogs processing machinery, complicating its removal from the digested liquid.
Finally, although digested, recycled PET material can be reacted with various hydrophobic materials to increase its molecular weight, many of the conventional hydrophobes used yield solid, thick, or opaque products; polyols that have substantial particulates; or polyols that separate into two phases. However, this is unacceptable for urethane formulations, which require polyester polyols to meet specifications for color, clarity, hydroxyl number, functionality, acid number, viscosity, and other properties.
Therefore, improved processes for producing sustainable polyols from recycled PET for the urethane industry are needed that not only minimize processing difficulties and improve sustainability but provide polyester polyols having the desired properties. It has unexpectedly been found that producing polyester polyols and plasticizers from a recycle stream of PTT or PET carpet, carpet fibers, yarn; PET containers, textiles, twine, string, or other PET or PTT recycled articles in an integrated recycling process using particularly defined hydrophobes and modifiers, can provide the required specifications for polyurethane and polyisocyanurate applications.